DESCRIPTION: The grant proposes to develop and validate a new assay for the identification of recent thymic emigrants. The assay is based upon a recent publication by Kong (Immunity 98) describing the detection of recently rearranged TCR DNA by the molecular identification of DNA deletion circles in chickens. The assay will be developed for human cells using the SCID-hu Thy/Li murine model. In addition, the authors plan to perform DNA excision circle analysis on T cells from HIV non-infected humans of varying ages and to characterize T cell subsets which are enriched for DNA deletion circles. Subsequently, the authors will attempt to monitor RTEs via DNA deletion circle positive cells in HIV infected humans at various stages of disease. Correlations with thymic mass by CT imaging in both normal and HIV infected hosts will also be made.